Temperature compensated oscillation circuit, oscillator, electronic apparatus, vehicle, and method of manufacturing oscillator

ABSTRACT

A temperature compensated oscillation circuit includes an oscillation circuit that oscillates a resonator, a fractional N-PLL circuit that multiplies frequency of an oscillation signal which is output by the oscillation circuit, on the basis of a frequency division ratio which is input, a temperature measurement unit that measures temperature, and a storage unit that stores a temperature correction table for correcting frequency temperature characteristics of the oscillation signal, in which the frequency division ratio of the fractional N-PLL circuit is set on the basis of a measurement value obtained by the temperature measurement unit and the temperature correction table.

BACKGROUND 1. Technical Field

The present invention relates to a temperature compensated oscillationcircuit, an oscillator, an electronic apparatus, a vehicle, and a methodof manufacturing the oscillator.

2. Related Art

Temperature compensated crystal oscillators (TCXO) include a quartzcrystal resonator and a temperature compensated oscillation circuit foroscillating the quartz crystal resonator, and the temperaturecompensated oscillation circuit compensates (temperature compensation)for a deviation (frequency deviation) from a desired frequency (nominalfrequency) of an oscillation frequency of the quartz crystal resonatorin a predetermined temperature range, thereby obtaining high frequencyaccuracy. Such a temperature compensated crystal oscillator (TCXO) isdisclosed in, for example, International Publication No. WO2004/025824.

However, in the temperature compensated crystal oscillator (TCXO) of therelated art as disclosed in International Publication No. WO2004/025824,a temperature sensor is required to have high accuracy of measurement inorder to realize high frequency accuracy (small frequency deviation) andis required to adjust so as to output a predetermined value at apredetermined temperature and to calculate a temperature compensationcoefficient in a state where the temperature of the oscillator isaccurately stabilized at a plurality of desired temperatures in amanufacturing step thereof, and thus it is difficult to reduce amanufacturing cost.

SUMMARY

An advantage of some aspects of the invention is to provide atemperature compensated oscillation circuit which is usable to realizean oscillator having a small frequency deviation depending ontemperature while reducing a manufacturing cost. In addition, accordingto some aspects of the invention, it is possible to provide anoscillator having a small frequency deviation depending on temperaturewhile reducing a manufacturing cost. In addition, according to someaspects of the invention, it is possible to provide an electronicapparatus and a vehicle which use the oscillator. In addition, accordingto some aspects of the invention, it is possible to provide a method ofmanufacturing the oscillator which is capable of realizing theoscillator having a small frequency deviation at a low cost.

The invention can be implemented as the following embodiments orapplication examples.

Application Example 1

A temperature compensated oscillation circuit according to thisapplication example includes an oscillation circuit that oscillates aresonator, a fractional N-PLL circuit that multiplies frequency of anoscillation signal which is output by the oscillation circuit, on thebasis of a frequency division ratio which is input, a temperaturemeasurement unit that measures temperature, and a storage unit thatstores a temperature correction table for correcting frequencytemperature characteristics of the oscillation signal, in which thefrequency division ratio of the fractional N-PLL circuit is set on thebasis of a measurement value obtained by the temperature measurementunit and the temperature correction table.

In the temperature compensated oscillation circuit according to theapplication example, the frequency division ratio of the fractionalN-PLL circuit for correcting the frequency temperature characteristic ofthe oscillation signal is set in association with the measurement valueobtained by the temperature measurement unit. Accordingly, when acorrespondence relationship between the actual temperature and atemperature measurement value does not fluctuate even when absolutemeasurement accuracy of the temperature measurement unit is low, it ispossible to output an oscillation signal with a small frequencydeviation of which the frequency temperature characteristics arecorrected. Therefore, it is possible to realize the oscillator having asmall frequency deviation depending on temperature by using thetemperature compensated oscillation circuit according to the applicationexample. In addition, since it is not also necessary to accuratelystabilize the temperature of the oscillator at a plurality of desiredtemperatures to thereby create the temperature correction table by usingthe temperature compensated oscillation circuit according to theapplication example, the number of manufacturing steps is reduced, andthus it is possible to reduce a manufacturing cost of the oscillator.

Application Example 2

The temperature compensated oscillation circuit according to theapplication example may further include a terminal, a control unit thatis capable of setting an update mode for updating the temperaturecorrection table, and a temperature correction table updating unit thatupdates the temperature correction table in the update mode on the basisof an output signal of the fractional N-PLL circuit and a referenceclock signal which is input from the terminal.

Application Example 3

In the temperature compensated oscillation circuit according to theapplication example, the temperature correction table updating unit maycalculate the frequency division ratio for bringing frequency of theoutput signal of the fractional N-PLL circuit close to frequency of thereference clock signal in the update mode, and may update thetemperature correction table on the basis of the frequency divisionratio.

The temperature compensated oscillation circuit according to theseapplication examples is set to be in the update mode, and thusautomatically updates (creates) the temperature correction table on thebasis of the reference clock signal which is input from the terminal.Therefore, an inspection apparatus does not need to perform a process ofcreating the temperature correction table and can simultaneouslymanufacture a plurality of oscillators by using the temperaturecompensated oscillation circuit according to the application example,and thus it is possible to reduce a manufacturing cost of theoscillator.

Application Example 4

The temperature compensated oscillation circuit according to theapplication example may further include a frequency division ratiocalculation unit that calculates the frequency division ratiocorresponding to the measurement value obtained by the temperaturemeasurement unit by using a plurality of the frequency division ratiosdescribed in the temperature correction table, in a case where thefrequency division ratio corresponding to the measurement value is notdescribed in the temperature correction table.

For example, in a case where the frequency division ratio correspondingto the measurement value obtained by the temperature measurement unit isnot described in the temperature correction table, the frequencydivision ratio calculation unit may perform complementary calculation ofthe frequency division ratio corresponding to the measurement valueobtained by the temperature measurement unit by using the frequencydivision ratios, corresponding to a measurement value smaller than themeasurement value obtained by the temperature measurement unit and ameasurement value larger than the measurement value obtained by thetemperature measurement unit, which are described in the temperaturecorrection table.

In the temperature compensated oscillation circuit according to thisapplication example, approximate calculation of a frequency divisionratio corresponding to a measurement value which is not described in thetemperature correction table is performed, and thus it is possible toreduce the size of the temperature correction table. Therefore, it ispossible to reduce a manufacturing cost of the oscillator by using thetemperature compensated oscillation circuit according to the applicationexample.

Application Example 5

An oscillator according to this application example includes any one ofthe above-described temperature compensated oscillation circuits, andthe resonator.

According to this application example, since the frequency divisionratio of the fractional N-PLL circuit for correcting the frequencytemperature characteristics of the oscillation signal is set inassociation with the measurement value obtained by the temperaturemeasurement unit, it is possible to realize the oscillator having asmall frequency deviation while reducing a manufacturing cost by usingthe temperature compensated oscillation circuit capable of outputtingthe oscillation signal having a small frequency deviation even when theaccuracy of measurement of the temperature measurement unit is low.

Application Example 6

An electronic apparatus according to this application example includesthe above-described oscillator.

Application Example 7

A vehicle according to this application example includes theabove-described oscillator.

According to these application examples, it is possible to realize theelectronic apparatus and vehicle, having higher reliability, whichinclude the oscillator having a small frequency deviation.

Application Example 8

A method of manufacturing an oscillator according to this applicationexample includes assembling the oscillator that includes a terminal, aresonator, and a temperature compensated oscillation circuit, thetemperature compensated oscillation circuit being provided with anoscillation circuit that oscillates the resonator, a fractional N-PLLcircuit that multiplies frequency of an oscillation signal which isoutput by the oscillation circuit on the basis of a frequency divisionratio which is input, a temperature measurement unit that measurestemperature, a storage unit that stores a temperature correction tablefor correcting frequency temperature characteristics of the oscillationsignal, a control unit that is capable of setting an update mode forupdating the temperature correction table, and a temperature correctiontable updating unit that updates the temperature correction table on thebasis of an output signal of the fractional N-PLL circuit and areference clock signal which is input from the terminal, and thefrequency division ratio of the fractional

N-PLL circuit being set on the basis of a measurement value obtained bythe temperature measurement unit and the temperature correction table,setting the temperature compensated oscillation circuit to be in theupdate mode, and inputting the reference clock signal to the terminal tothereby change temperature of the oscillator in a predetermined range.

According to the method of manufacturing an oscillator according to thisapplication example, the temperature compensated oscillation circuit isset to be in the update mode, and thus the temperature correction tablefor correcting frequency temperature characteristics of the oscillationsignal in a predetermined temperature range is automatically updated(created) on the basis of the reference clock signal. Therefore, aninspection apparatus does not need to perform a process of creating thetemperature correction table and can simultaneously manufacture aplurality of oscillators by using the temperature compensatedoscillation circuit according to the application example, and thus it ispossible to reduce a manufacturing cost of the oscillator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating an oscillator according tothis embodiment.

FIG. 2 is a cross-sectional view of the oscillator according to thisembodiment.

FIG. 3 is a bottom view of the oscillator according to this embodiment.

FIG. 4 is a functional block diagram of an oscillator according to afirst embodiment.

FIG. 5 is a diagram illustrating an example of frequency temperaturecharacteristics of an output signal of an oscillation circuit.

FIG. 6 is a diagram illustrating an example of temperaturecharacteristics of an output signal of a temperature measurement unit.

FIG. 7 is a diagram illustrating an example of a configuration of atemperature correction table according to the first embodiment.

FIG. 8 is a diagram illustrating a configuration example of a fractionalN-PLL circuit.

FIG. 9 is a flow chart illustrating an example of a procedure of atemperature correction table updating process according to the firstembodiment.

FIG. 10 is a diagram illustrating an example of signal waveforms in thetemperature correction table updating process.

FIG. 11 is a flow chart illustrating an example of a method ofmanufacturing the oscillator according to this embodiment.

FIG. 12 is a diagram illustrating an example of signal waveforms ofexternal terminals of the oscillator.

FIG. 13 is a functional block diagram of an oscillator according to asecond embodiment.

FIG. 14 is a diagram illustrating an example of a configuration of atemperature correction table according to the second embodiment.

FIG. 15 is a flow chart illustrating an example of a procedure of atemperature correction table updating process according to the secondembodiment.

FIG. 16 is a functional block diagram of an electronic apparatusaccording to this embodiment.

FIG. 17 is a diagram illustrating an example of the exterior of anelectronic apparatus according to this embodiment.

FIG. 18 is a diagram illustrating an example of a vehicle according tothis embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be described indetail with reference to the accompanying drawings. Meanwhile, theembodiments described below are not unduly limited to the disclosure ofthe invention described in the appended claims. In addition, all theconfigurations described below are not necessarily essential componentsof the invention.

1. Oscillator 1-1. First Embodiment Configuration of Oscillator

FIGS. 1 to 3 are diagrams illustrating an example of a structure of anoscillator 1 according to this embodiment. FIG. 1 is a perspective viewof the oscillator 1, and FIG. 2 is a cross-sectional view taken alongline A-A′ of FIG. 1. In addition, FIG. 3 is a bottom view of theoscillator 1.

The oscillator 1 of this embodiment is a temperature compensatedoscillator, and is configured to include a temperature compensatedoscillation circuit 2, a resonator 3, a package 4, a lid (cover) 5, andexternal terminals (external electrodes) 6, as illustrated in FIGS. 1 to3. In this embodiment, it is assumed that the resonator 3 is a quartzcrystal resonator, but may be, for example, a surface acoustic wave(SAW) resonator, any of other piezoelectric resonators, micro electromechanical systems (MEMS) resonator, or the like. In addition, examplesof a substrate material of the resonator 3 may include a piezoelectricmaterial such as piezoelectric single crystal, for example, quartzcrystal, lithium tantalate, and lithium niobate, or piezoelectricceramics, for example, lead zirconate titanate, a silicon semiconductormaterial, and the like. As an excitation unit of the resonator 3, a unitbased on a piezoelectric effect may be used, or electrostatic drivingbased on a Coulomb force may be used.

The package 4 accommodates the temperature compensated oscillationcircuit 2 and the resonator 3 in the same space. Specifically, thepackage 4 is provided with a concave portion, and the concave portion iscovered with the lid 5, thereby configuring a housing chamber 7.Wirings, not shown in the drawing, for electrically connecting twoterminals (an XG terminal and an XD terminal of FIG. 3 to be describedlater) of the temperature compensated oscillation circuit 2 and twoterminals (excitation electrodes 3 a and 3 b) of the resonator 3 areprovided inside the package 4 or on the surface of the concave portion.In addition, wirings, not shown in the drawing, for electricallyconnecting the terminals of the temperature compensated oscillationcircuit 2 and the corresponding external terminals 6 are provided insidethe package 4 or on the surface of the concave portion.

The resonator 3 includes the excitation electrodes 3 a and 3 b, formedof a metal, on the front and rear surfaces thereof, and oscillates at adesired frequency (target frequency required for the oscillator 1) basedon the shape or mass of the resonator 3 including the excitationelectrodes 3 a and 3 b.

As illustrated in FIG. 3, the oscillator 1 is provided with fourexternal terminals 6 of an external terminal VCC which is a power supplyterminal, an external terminal GND which is a ground terminal, anexternal terminal OE which is an input and output terminal, and anexternal terminal OUT which is an input and output terminal, on thebottom surface thereof (rear surface of the package 4). A power supplyvoltage is supplied to the external terminal VCC, and the externalterminal GND is grounded.

FIG. 4 is a functional block diagram of the oscillator 1 according tothis embodiment. As illustrated in FIG. 4, the oscillator 1 of a firstembodiment is configured to include the temperature compensatedoscillation circuit 2 and the resonator 3. The temperature compensatedoscillation circuit 2 is provided with a VCC terminal which is a powersupply terminal, a GND terminal which is a ground terminal, an OEterminal which is an input and output terminal, an OUT terminal which isan input and output terminal, and an XG terminal and an XD terminalwhich are terminals connected to the resonator 3. The VCC terminal, theGND terminal, the OE terminal, and the OUT terminal are exposed to thesurface of the temperature compensated oscillation circuit 2, and arerespectively connected to the external terminals VCC, GND, OE, and OUTof the oscillator 1 which are provided in the package 4. In addition,the XG terminal is connected to one end (one terminal) of the resonator3, and the XD terminal is connected to the other end (the otherterminal) of the resonator 3.

In this embodiment, the temperature compensated oscillation circuit 2 isconfigured to include an oscillation circuit 21, a fractional N-PLLcircuit 22, an output circuit 23, a control unit 24, a temperaturemeasurement unit 25, a storage unit 26, and a temperature correctiontable updating unit 27. Meanwhile, the temperature compensatedoscillation circuit 2 may be configured such that a portion of thesecomponents is omitted or changed or other components are added.

In this embodiment, the temperature compensated oscillation circuit 2 isconfigured as an integrated circuit (IC) of one chip, but may beconstituted by an integrated circuit (IC) of a plurality of chips or maybe partially constituted by a discrete component.

The oscillation circuit 21 oscillates the resonator 3 by amplifying anoutput signal of the resonator 3 which is input from the XG terminal ofthe temperature compensated oscillation circuit 2 and feeding back theamplified signal to the resonator 3 through the XD terminal of thetemperature compensated oscillation circuit 2, and outputs anoscillation signal (clock signal OSCCLK) based on the oscillation of theresonator 3. For example, the oscillation circuit constituted by theresonator 3 and the oscillation circuit 21 may be various types ofoscillation circuits such as a pierced oscillation circuit, aninverter-type oscillation circuit, a Colpitts oscillation circuit, and aHartley oscillation circuit.

A frequency f_(OSCCLK) of the output signal (clock signal OSCCLK) of theoscillation circuit 21 has frequency temperature characteristics basedon temperature characteristics of the resonator 3, and the like. FIG. 5is a diagram illustrating an example of frequency temperaturecharacteristics of the output signal (clock signal OSCCLK) of theoscillation circuit 21. In FIG. 5, the horizontal axis representstemperature (unit: ° C.), and the vertical axis represents a frequency(unit: Hz). In the example of FIG. 5, the frequency f_(OSCCLK) of theclock signal OSCCLK changes in the form of a substantially cubic curvewith respect to temperature with reference temperature (for example, atemperature of approximately +25° C.) as a inflection point, and is notconstant in a temperature range (operation guarantee temperature range)(for example, −40° C. to +85° C.) in which the operation of theoscillator 1 is guaranteed.

Referring back to FIG. 4, the fractional N-PLL circuit 22 multiplies thefrequency of the oscillation signal (clock signal OSCCLK) which isoutput by the oscillation circuit 21 on the basis of a frequencydivision ratio which is input. Specifically, the fractional N-PLLcircuit 22 generates a clock signal PLLCLK obtained by multiplying thefrequency f_(OSCCLK) of the clock signal OSCCLK which is output by theoscillation circuit 21, on the basis of a frequency division ratio whichis input from a temperature correction table 261 stored in the storageunit 26. Here, when an integer portion (integer frequency divisionratio) of the frequency division ratio is set to be N and a fractionportion (fraction frequency division ratio) is set to be F/M, therelation of the following expression (1) is established between thefrequency f_(OSCCLK) of the clock signal OSCCLK and a frequencyf_(PLLCLK) Of the clock signal PLLCLK.

$\begin{matrix}{f_{PLLCLK} = {\left( {N + \frac{F}{M}} \right)f_{OSCCLK}}} & (1)\end{matrix}$

In this embodiment, the fractional N-PLL circuit 22 functions as acircuit that corrects frequency temperature characteristics (see FIG. 5)of the output signal (clock signal OSCCLK) of the oscillation circuit21, on the basis of the integer frequency division ratio N and thefraction frequency division ratio F/M which are output from thetemperature correction table 261. That is, the integer frequencydivision ratio N and the fraction frequency division ratio F/M which areoutput from the temperature correction table 261 change depending on atemperature, and the fractional N-PLL circuit 22 operates so as to bringthe frequency f_(PLLCLK) of the clock signal PLLCLK close to a targetfrequency in an operation guarantee temperature range (for example, −40°C. to +85° C.), on the basis of the integer frequency division ratio Nand the fraction frequency division ratio F/M. As described later, thefrequency division ratio (an integer frequency division ratio N and afraction frequency division ratio F/M) of the fractional N-PLL circuit22 is set on the basis of a measurement value (temperature measurementvalue DT) of the temperature measurement unit 25 and the temperaturecorrection table 261.

Meanwhile, the fractional N-PLL circuit 22 may be a circuit thatcorrects the frequency temperature characteristics (see FIG. 5) of theclock signal OSCCLK, converts the frequency f_(OSCCLK) into apredetermined frequency f_(PLLCLK) (for example, a frequency two, ½ orthe like times frequency f_(OSCCLK)), and outputs the convertedfrequency.

The output circuit 23 receives an input of the clock signal PLLCLK whichis output by the fractional N-PLL circuit 22 to thereby generate anoscillation signal of which the amplitude thereof is adjusted to adesired level. The oscillation signal generated by the output circuit 23is output to the outside of the oscillator 1 through the OUT terminal ofthe temperature compensated oscillation circuit 2 and the externalterminal OUT of the oscillator 1.

The control unit 24 is a circuit that controls operations of theoscillation circuit 21, the output circuit 23, and the temperaturecorrection table updating unit 27. In addition, the control unit 24 canset an operation mode of the oscillator 1 (temperature compensatedoscillation circuit 2) to each of a plurality of modes including anexternal communication mode, a normal operation mode, and a temperaturecorrection table update mode (an example of an update mode for updatinga temperature correction table), on the basis of a control signal whichis input through a terminal of the temperature compensated oscillationcircuit 2 from an external terminal of the oscillator 1, and performscontrol based on the set operation mode. In this embodiment, in a casewhere a control signal having a predetermined pattern is input from theexternal terminal OE of the oscillator 1 (the OE terminal of thetemperature compensated oscillation circuit 2) within a predeterminedperiod of time after a power supply voltage is started to be supplied tothe external terminal VCC of the oscillator 1 (VCC terminal of thetemperature compensated oscillation circuit 2) (that is, within apredetermined period of time after a power supply is turned on), thecontrol unit 24 sets an operation mode of the oscillator 1 (temperaturecompensated oscillation circuit 2) to be an external communication modeafter the predetermined period of time elapses. For example, the controlunit 24 may set a period of time between when the resonator 3 starts tooscillate by the turn-on of the power supply of the oscillator 1(temperature compensated oscillation circuit 2) and when it is detectedthat the oscillation is stabilized (for example, the clock signal OSCCLKhas a desired amplitude) to be the predetermined period of time, and maydetermine that the predetermined period of time has elapsed when acounted number of pulses of the clock signal OSCCLK reaches apredetermined value. In addition, for example, the control unit 24 maymeasure the predetermined period of time on the basis of an outputsignal of an RC time constant circuit that starts to operate when thepower supply of the oscillator 1 (temperature compensated oscillationcircuit 2) is turned on.

In the external communication mode, a serial clock signal and a serialdata signal are input in synchronization with each other as controlsignals from the external terminals OE and OUT of the oscillator 1 (OEand OUT terminals of the temperature compensated oscillation circuit 2),and the control unit 24 samples the serial data signal for each edge ofthe serial clock signal according to, for example, the standard of anI²C (Inter-Integrated Circuit) bus and performs processing such as thesetting of operation modes and the setting of control data in eachoperation mode on the basis of the sampled command and data. Forexample, the control unit 24 samples a command for making the operationmode of the oscillator 1 (temperature compensated oscillation circuit 2)transition to a mode (the normal operation mode, the temperaturecorrection table update mode, or the like) to thereby set the operationmode of the oscillator 1 (temperature compensated oscillation circuit 2)to the modes.

In a case where a control signal (output enable signal) which is inputfrom the external terminal OE of the oscillator 1 (the OE terminal ofthe temperature compensated oscillation circuit 2) is in an active state(for example, a high level) in the normal operation mode, the controlunit 24 performs control so as to operate the oscillation circuit 21 andoutput circuit 23. Thereby, an oscillation signal is output from theexternal terminal OUT of the oscillator 1 (the OUT terminal of thetemperature compensated oscillation circuit 2).

In addition, in a case where a control signal (output enable signal)which is input from the external terminal OE of the oscillator 1 (the OEterminal of the temperature compensated oscillation circuit 2) is in anon-active state (for example, a low level) in the normal operationmode, the control unit 24 performs control so as to operate theoscillation circuit 21 and to stop the operation of the output circuit23 when standby bit data stored in a non-volatile memory, not shown inthe drawing, is in a non-active state (for example, zero) , and performscontrol so as to stop the operation of the oscillation circuit 21 andthe output circuit 23 when the standby bit data is in an active state(for example, 1). In any of these cases, the output of the oscillationsignal from the external terminal OUT of the oscillator 1 (the OUTterminal of the temperature compensated oscillation circuit 2) isstopped.

Meanwhile, in a case where a control signal having a predeterminedpattern is not input from the external terminal OE of the oscillator 1(the OE terminal of the temperature compensated oscillation circuit 2)within a predetermined period of time after a power supply is turned on,the control unit 24 directly sets the operation mode of the oscillator 1(temperature compensated oscillation circuit 2) to the normal operationmode without setting the operation mode to the external communicationmode after the predetermined period of time elapses.

In addition, the control unit 24 performs control so as to operate theoscillation circuit 21, the output circuit 23, and the temperaturecorrection table updating unit 27 in the temperature correction tableupdate mode. Meanwhile, the control unit 24 performs control so as notto operate the temperature correction table updating unit 27 in theexternal communication mode and the normal operation mode.

The temperature measurement unit 25 is a circuit that measurestemperature. In this embodiment, the temperature measurement unit 25converts the measured temperature into a temperature measurement valueDT which is a digital value, and outputs the converted value to thestorage unit 26. For example, the temperature measurement unit 25 may beconfigured to include a temperature sensor (for example, a temperaturesensor using temperature characteristics of a bandgap reference circuit,or the like) which has a voltage changing depending on temperature andan analog to digital (A/D) converter that converts an output signal ofthe temperature sensor into a temperature measurement value DT, or maybe configured to include an oscillation unit having an oscillationfrequency changing depending on temperature and a measurement unit thatmeasures an oscillation frequency of the oscillation unit and outputs atemperature measurement value DT based on a measurement result.

FIG. 6 is a diagram illustrating an example of temperaturecharacteristics of an output signal (temperature measurement value DT)of the temperature measurement unit 25. In FIG. 6, the horizontal axisrepresents temperature (unit: ° C.), and the vertical axis representsthe temperature measurement value DT. In the example of FIG. 6, thetemperature measurement value DT is a 8-bit digital value (0 to 255),and changes at a substantially fixed ratio in a stepwise manner withrespect to a change in temperature in at least an operation guaranteetemperature range (for example, −40° C. to +85° C.). That is, in theexample of FIG. 6, the temperature measurement unit 25 outputs the 8-bittemperature measurement value DT having a fixed resolution.

Referring back to FIG. 4, the storage unit 26 stores the temperaturecorrection table 261 for correcting frequency temperaturecharacteristics of the oscillation signal (clock signal OSCCLK) which isoutput by the oscillation circuit 21. Specifically, the storage unit 26includes a non-volatile memory, not shown in the drawing, and thetemperature correction table 261 is stored in the non-volatile memory.Examples of the non-volatile memory to be applied may include anelectrically erasable programmable read-only memory (EEPROM), a flashmemory, and the like.

In this embodiment, the temperature correction table 261 is a table inwhich a correspondence relationship between the temperature measurementvalue DT which is output by the temperature measurement unit 25 and thefrequency division ratio (an integer frequency division ratio N and afraction frequency division ratio F/M) of the fractional N-PLL circuit22 is described. The storage unit 26 selects the integer frequencydivision ratio N and the fraction frequency division ratio F/M which aredescribed (stored) in association with the 8-bit temperature measurementvalue DT which is output by the temperature measurement unit 25 in thetemperature correction table 261, and outputs the selected ratios to thefractional N-PLL circuit 22.

FIG. 7 is a diagram illustrating an example of a configuration of thetemperature correction table 261. In the example of FIG. 7, acorrespondence relationship between a 8-bit temperature measurementvalue DT (0 to 255) which is also used as addresses 0 to 255 of 8 bits,an integer frequency division ratio N (X0 to X255), and a fractionfrequency division ratio F/M (Y0 to Y255) is described (stored). In theexample of FIG. 7, in the temperature correction table 261, the integerfrequency division ratio N and the fraction frequency division ratio F/Mwhich are stored in the address are read out using the temperaturemeasurement value DT which is output by the temperature measurement unit25 as a read-out address. Thereby, an appropriate integer frequencydivision ratio N and fraction frequency division ratio F/M based ontemperature are output to the fractional N-PLL circuit 22, and frequencytemperature characteristics of the oscillation circuit 21 are correctedin the fractional N-PLL circuit 22.

Referring back to FIG. 4, the temperature correction table updating unit27 performs a process of updating the temperature correction table 261(temperature correction table updating process) on the basis of theoutput signal (clock signal PLLCLK) of the fractional N-PLL circuit 22and a reference clock signal REFCLK which is input from the terminal ofthe temperature compensated oscillation circuit 2 in the temperaturecorrection table update mode. Specifically, the temperature correctiontable updating unit 27 calculates a frequency division ratio forbringing the frequency of the output signal (clock signal PLLCLK) of thefractional N-PLL circuit 22 close to the frequency of the referenceclock signal REFCLK in the temperature correction table update mode, andupdates the temperature correction table 261 on the basis of thefrequency division ratio and the temperature measurement value DT whichis output by the temperature measurement unit 25. In this embodiment, inthe temperature correction table update mode, the reference clock signalREFCLK having a sufficiently small frequency deviation with respect to atarget frequency (sufficiently satisfying frequency accuracy requiredfor the oscillator 1) is input from the external terminal OE of theoscillator 1 (the OE terminal of the temperature compensated oscillationcircuit 2), and the ambient temperature of the oscillator 1 graduallychanges in a temperature range (for example, −45° C. to +90° C.)including an operation guarantee temperature range (for example, −40° C.to +85° C.) of the oscillator 1, thereby causing the temperaturecorrection table updating unit 27 to perform the temperature correctiontable updating process. Details of this temperature correction tableupdating process will be described later.

Configuration of Fractional N-PLL Circuit

FIG. 8 is a diagram illustrating a configuration example of thefractional N-PLL circuit 22 according to this embodiment. As illustratedin FIG. 8, the fractional N-PLL circuit 22 is configured to include aphase comparator 221, a charge pump 222, a low-pass filter 223, avoltage control oscillation circuit 224, a frequency division circuit225, a clock generation circuit 226, a delta-sigma modulation circuit227, and an addition and subtraction circuit 228.

The phase comparator 221 compares a phase difference in the clock signalOSCCLK which is output by the oscillation circuit 21 with a phasedifference in a clock signal FBCLK which is output by the frequencydivision circuit 225, and outputs a comparison result as a pulsevoltage.

The charge pump 222 converts the pulse voltage which is output by thephase comparator 221 into a current, and the low-pass filter 223 smoothsthe current which is output by the charge pump 222 and converts thesmoothed current into a voltage.

The voltage control oscillation circuit 224 outputs the clock signalPLLCLK having a frequency changing depending on a control voltage byusing an output voltage of the low-pass filter 223 as the controlvoltage. The voltage control oscillation circuit 224 can be realized byany of various types of oscillation circuits such as an LC oscillationcircuit constituted by an inductance element such as a coil and acapacitive element such as a capacitor, an oscillation circuit using apiezoelectric resonator such as a quartz crystal resonator, and thelike.

The frequency division circuit 225 outputs the clock signal FBCLKobtained by dividing the frequency of the clock signal PLLCLK, which isoutput by the voltage control oscillation circuit 224, by an integer byusing an output signal of the addition and subtraction circuit 228 as afrequency division ratio (integer frequency division ratio).

The clock generation circuit 226 generates a clock signal DSMCLK byusing the clock signal FBCLK, and outputs the generated clock signal.For example, the clock generation circuit 226 may output the clocksignal FBCLK as the clock signal DSMCLK as it is, and may output theclock signal DSMCLK obtained by dividing the frequency of the clocksignal FBCLK by an integer.

The delta-sigma modulation circuit 227 performs delta-sigma modulationin which the fraction frequency division ratio F/M which is input fromthe temperature correction table 261 is integrated to be quantized, insynchronization with the clock signal DSMCLK which is output by theclock generation circuit 226.

The addition and subtraction circuit 228 adds and subtracts adelta-sigma modulation signal which is output by the delta-sigmamodulation circuit 227 and the integer frequency division ratio N whichis input from the temperature correction table 261 to and from eachother. The output signal of the addition and subtraction circuit 228 isinput to the frequency division circuit 225. Regarding the output signalof the addition and subtraction circuit 228, a plurality of integerfrequency division ratios in a range near the integer frequency divisionratio N change in time series, and the time average value thereofcoincides with N+F/M. In a steady state in which the phase of the clocksignal OSCCLK and the phase of the clock signal FBCLK are synchronizedwith each other, the frequency f_(PLLCLK) of the clock signal PLLCLK andthe frequency f_(OSCCLK) of the clock signal OSCCLK satisfy the relationof Expression (1), and thus the frequency f_(PLLCLK) of the clock signalPLLCLK approximates to the target frequency.

For example, in a case where the target frequency of the clock signalPLLCLK is 100 MHz, a time average value of an output signal of theaddition and subtraction circuit 228, that is, a time average value of afrequency division ratio of the frequency division circuit 225 isrequired to be approximately 1.0001 when the frequency of the clocksignal OSCCLK is 99.99 MHz at a certain temperature TA. Therefore, inthe temperature correction table 261, the integer frequency divisionratio N associated with the temperature TA is set to 1, and the fractionfrequency division ratio F/M is set to approximately 0.0001.

Temperature Correction Table Updating Process

As described above, the temperature correction table 261 is stored inthe non-volatile memory of the storage unit 26, but an initial value ofeach bit of the non-volatile memory is not fixed. Therefore, in a stepof manufacturing the oscillator 1, it is necessary to write the integerfrequency division ratio N and the fraction frequency division ratio F/Menabling frequency temperature characteristics of the clock signalOSCCLK to be corrected in the address of the storage unit 26 storing thetemperature correction table 261. In this embodiment, when the controlunit 24 sets the operation mode of the oscillator 1 (temperaturecompensated oscillation circuit 2) to be the temperature correctiontable update mode, the temperature correction table updating unit 27performs a temperature correction table updating process of updating theinteger frequency division ratio N and the fraction frequency divisionratio F/M which are stored in the temperature correction table.

FIG. 9 is a flow chart illustrating an example of a procedure of thetemperature correction table updating process performed by thetemperature correction table updating unit 27.

As illustrated in FIG. 9, when the operation mode of the oscillator 1(temperature compensated oscillation circuit 2) is set to be thetemperature correction table update mode, the temperature correctiontable updating unit 27 first compares the frequency f_(PLLCLK) of theclock signal PLLCLK with a frequency f_(REFCLK) of the reference clocksignal REFCLK (S100). For example, the temperature correction tableupdating unit 27 may compare the frequencies with each other by countingthe number of pulses of the reference clock signal REFCLK which isincluded in a period of time (frequency comparison period) in which apredetermined number of pulses of the clock signal PLLCLK is generated,or may compare the frequencies with each other by counting the number ofpulses of the clock signal PLLCLK which is included in a period of time(frequency comparison period) in which a predetermined number of pulsesof the reference clock signal REFCLK is generated.

Next, the temperature correction table updating unit 27 calculates afrequency division ratio (an integer frequency division ratio N and afraction frequency division ratio F/M) for bringing the frequencyf_(PLLCLK) of the clock signal PLLCLK close to the frequency f_(REFCLK)of the reference clock signal REFCLK, on the basis of a result of thecomparison between the frequencies which is performed in Step S100(S110).

Next, the temperature correction table updating unit 27 acquires thetemperature measurement value DT which is output by the temperaturemeasurement unit 25, writes the frequency division ratio (the integerfrequency division ratio N and the fraction frequency division ratioF/M) which is calculated in Step S110 in the storage unit 26 inassociation with the temperature measurement value DT, and updates thetemperature correction table 261 (S120).

The temperature correction table updating unit 27 continuously performsthe processes of steps 100 to S120 while the temperature correctiontable update mode is continued (Y of S130), and terminates the processeswhen the temperature correction table update mode is terminated (N ofS130).

Meanwhile, in the flow chart of FIG. 9, a portion of the processes ofSteps S100 to S130 may be appropriately omitted or changed, or otherprocesses may be added. In addition, in the flowchart of FIG. 9, theorder of the processes of Steps S100 to S130 may be changed in apossible range.

FIG. 10 is a diagram illustrating an example of signal waveforms in acase where the temperature correction table updating unit 27 performsthe temperature correction table updating process according to theprocedure illustrated in FIG. 9. In the example of FIG. 10, thetemperature correction table 261 is configured as illustrated in FIG. 7,and it is assumed that all values X0 to X255 of the integer frequencydivision ratio N are initialized to 1 and all values Y0 to Y255 of thefraction frequency division ratio F/M are initialized to zero when thetemperature correction table update mode is started.

In the example of FIG. 10, the ambient temperature of the oscillator 1is, for example, approximately −45° and the temperature measurementvalue DT is set to zero at time t0 when the temperature correction tableupdate mode is started. Therefore, the value of the integer frequencydivision ratio N which is output to the fractional N-PLL circuit 22 fromthe temperature correction table 261 of the storage unit 26 is set to X0(=1), and the value of the fraction frequency division ratio F/M is setto Y0 (=0). For this reason, the frequency f_(PLLCLK) of the clocksignal PLLCLK coincides with the frequency f_(OSCCLK) of the clocksignal OSCCLK which is output by the oscillation circuit 21 and has agreat frequency deviation caused by temperature characteristics of theresonator 3.

At time t1 after the frequency comparison period (period of time of theprocess of Step S100 of FIG. 9) elapses, the temperature measurementvalue DT remains being set to zero, and thus the value X0 of the integerfrequency division ratio N and the value Y0 of the fraction frequencydivision ratio F/M which correspond to the temperature measurement valueDT=0 of the temperature correction table 261 are updated (overwritten)on the basis of the value of the integer frequency division ratio N andthe value of the fraction frequency division ratio F/M which arecalculated by the temperature correction table updating unit 27.Thereby, the integer frequency division ratio N and the fractionfrequency division ratio F/M which are output to the fractional N-PLLcircuit 22 from the temperature correction table 261 are also updated,and the frequency f_(PLLCLK) of the clock signal PLLCLK approximates tothe frequency f_(REFCLK) of the reference clock signal REFCLK.

Further, at time t2 after the frequency comparison period elapses, thetemperature measurement value DT remains being set to zero, and thus thevalue X0 of the integer frequency division ratio N and the value Y0 ofthe fraction frequency division ratio F/M which correspond to thetemperature measurement value DT=0 of the temperature correction table261 are further updated (overwritten) on the basis of the value of theinteger frequency division ratio N and the value of the fractionfrequency division ratio F/M which are calculated by the temperaturecorrection table updating unit 27. Thereby, the integer frequencydivision ratio N and the fraction frequency division ratio F/M which areoutput to the fractional N-PLL circuit 22 from the temperaturecorrection table 261 are also updated, and the frequency f_(PLLCLK) ofthe clock signal PLLCLK further approximates to the frequency f_(REFCLK)of the reference clock signal REFCLK.

Further, at time t3 after the frequency comparison period elapses, thetemperature measurement value DT remains being set to zero, and thus thevalue X0 of the integer frequency division ratio N and the value Y0 ofthe fraction frequency division ratio F/M which correspond to thetemperature measurement value DT=0 of the temperature correction table261 are further updated (overwritten) on the basis of the value of theinteger frequency division ratio N and the value of the fractionfrequency division ratio F/M which are calculated by the temperaturecorrection table updating unit 27. Thereby, the integer frequencydivision ratio N and the fraction frequency division ratio F/M which areoutput to the fractional N-PLL circuit 22 from the temperaturecorrection table 261 are also updated, and the frequency f_(PLLCLK) ofthe clock signal PLLCLK further approximates to the frequency f_(REFCLK)of the reference clock signal REFCLK.

Thereafter, at time t4, the temperature measurement value DT changesfrom 0 to 1 due to a rise in the ambient temperature of the oscillator1, and the value of the integer frequency division ratio N and the valueof the fraction frequency division ratio F/M which are output to thefractional N-PLL circuit 22 from the temperature correction table 261 ofthe storage unit 26 change to X1 (=1) and Y1 (=0), respectively. Forthis reason, the frequency f_(PLLCLK) of the clock signal PLLCLKcoincides with the frequency f_(OSCCLK) of the clock signal OSCCLK whichis output by the oscillation circuit 21 and has a great frequencydeviation caused by temperature characteristics of the resonator 3.

Next, at time t5 after the frequency comparison period elapses, thetemperature measurement value DT is 1, and thus the value X1 of theinteger frequency division ratio N and the value Y1 of the fractionfrequency division ratio F/M which correspond to the temperaturemeasurement value DT=1 of the temperature correction table 261 areupdated (overwritten) on the basis of the value of the integer frequencydivision ratio N and the value of the fraction frequency division ratioF/M which are calculated by the temperature correction table updatingunit 27. Thereby, the integer frequency division ratio N and thefraction frequency division ratio F/M which are output to the fractionalN-PLL circuit 22 from the temperature correction table 261 are alsoupdated, and the frequency f_(PLLCLK) of the clock signal PLLCLKapproximates to the frequency f_(REFCLK) of the reference clock signalREFCLK.

Further, at time t6 after the frequency comparison period elapses, thetemperature measurement value DT remains being set to 1, and thus thevalue X1 of the integer frequency division ratio N and the value Y1 ofthe fraction frequency division ratio F/M which correspond to thetemperature measurement value DT=1 of the temperature correction table261 are further updated (overwritten) on the basis of the value of theinteger frequency division ratio N and the value of the fractionfrequency division ratio F/M which are calculated by the temperaturecorrection table updating unit 27. Thereby, the integer frequencydivision ratio N and the fraction frequency division ratio F/M which areoutput to the fractional N-PLL circuit 22 from the temperaturecorrection table 261 are also updated, and the frequency f_(PLLCLK) ofthe clock signal PLLCLK further approximates to the frequency f_(REFCLK)of the reference clock signal REFCLK.

Hereinafter, similarly, when the temperature measurement value DT is kwhile the temperature correction table update mode is continued, a valueXk of the integer frequency division ratio N and a value Yk of thefraction frequency division ratio F/M of the temperature correctiontable 261 are sequentially updated.

Method of Manufacturing Oscillator

FIG. 11 is a flow chart illustrating an example of a method ofmanufacturing an oscillator according to this embodiment. The method ofmanufacturing an oscillator according to this embodiment includes stepsS10 to S30 illustrated in FIG. 11. However, in the method ofmanufacturing an oscillator according to this embodiment, a portion ofsteps S10 to S30 may be omitted or changed, or other steps may be added.In addition, FIG. 12 is a diagram illustrating an example of signalwaveforms of the external terminals VCC, GND, OE, and OUT of theoscillator 1 in steps S10 and S20 of the flow chart of FIG. 11.

As illustrated in FIG. 11, in this embodiment, first, the oscillator 1including the resonator 3 and the temperature compensated oscillationcircuit 2 is assembled (step S10).

Next, a control signal is input to the external terminal of theoscillator 1, and the operation mode of the oscillator 1 (temperaturecompensated oscillation circuit 2) is set to be a temperature correctiontable update mode (step S20). That is, as illustrated in FIG. 12, asignal having a predetermined pattern determined in advance is input tothe external terminal OE of the oscillator 1 to set the operation modeof the oscillator 1 (temperature compensated oscillation circuit 2) tobe an external communication mode within a predetermined period of timeafter a power supply is turned on, and a serial clock signal and aserial data signal (temperature correction table update command) arerespectively input from the external terminals OE and OUT in theexternal communication mode to set the operation mode of the oscillator1 (temperature compensated oscillation circuit 2) to be a temperaturecorrection table update mode.

Next, the reference clock signal REFCLK is input to the externalterminal OE of the oscillator 1 (the OE terminal of the temperaturecompensated oscillation circuit 2) to change the temperature of theoscillator 1 in a predetermined range (step S30). That is, asillustrated in FIG. 12, the ambient temperature of the oscillator 1 isgradually changed from a lower limit to an upper limit (or from theupper limit to the lower limit) of a temperature range (for example,−45° C. to +90° C.) including an operation guarantee temperature range(for example, −40° C. to +85° C.) of the oscillator 1 in a state wherethe reference clock signal REFCLK is input to the external terminal OEof the oscillator 1. Thereby, the temperature correction table 261enabling frequency temperature characteristics of the clock signalOSCCLK to be corrected in the operation guarantee temperature range (forexample, −40° C. to +85° C.) of the oscillator 1 is created. At thistime, it is not necessary to stabilize the ambient temperature of theoscillator 1 for each predetermined temperature. However, when the speedof the change in the ambient temperature of the oscillator 1 isexcessively high, a frequency division ratio of a portion of thetemperature correction table 261 is not set to an appropriate value, andthus there is a possibility that sufficient frequency accuracy is notobtained. Therefore, it is preferable to change the ambient temperatureof the oscillator 1 in a sufficiently gradual manner. For example, timerequired for the calculation of a value of an appropriate frequencydivision ratio with respect to each of 8-bit temperature measurementvalues DT (0 to 255) is less than one second, and thus the temperaturemay be changed for approximately several minutes while maintaining aconstant speed from −40° C. to +85° C.

Meanwhile, in the flow chart of FIG. 11, a plurality of oscillators 1may be assembled in step S10, the operation modes of the plurality ofoscillators 1 may be set to be a temperature correction table updatemode instep S20, and step S30 may be simultaneously performed on theplurality of oscillators 1. In this manner, the plurality of oscillators1 can simultaneously create an appropriate temperature correction table261, and thus it is possible to reduce a total number of manufacturingsteps and to reduce a manufacturing cost of the oscillator 1 as thenumber of oscillators 1 increases. Alternatively, there is a smallincrease in the number of manufacturing steps for each oscillator 1 inspite of an increase in a total number of manufacturing steps bychanging the ambient temperature of the plurality of oscillators 1 in amore gradual manner, and thus it is possible to improve the frequencyaccuracy of the oscillator 1 while suppressing an increase in cost.

Operational Effects

As described above, according to the oscillator 1 of the firstembodiment, in the temperature compensated oscillation circuit 2, afrequency division ratio of the fractional N-PLL circuit 22 forcorrecting frequency temperature characteristics of the clock signalOSCCLK is set in association with the temperature measurement value DTwhich is output by the temperature measurement unit 25, and thus it ispossible to realize the oscillator having a small frequency deviationdepending on temperature when a correspondence relationship between theactual temperature and the temperature measurement value DT does notfluctuate in spite of low accuracy of measurement of the temperaturemeasurement unit 25. In addition, according to the first embodiment,since a waiting time for accurately stabilizing the ambient temperatureof the oscillator 1 at a plurality of desired temperatures is notnecessary in order to create the temperature correction table 261, thenumber of manufacturing steps is decreased, and thus it is possible toreduce a manufacturing cost of the oscillator 1.

In particular, the oscillator 1 of the first embodiment is set to be ina temperature correction table update mode to thereby automaticallyupdate (create) the temperature correction table 261 on the basis of thereference clock signal REFCLK which is input from the external terminalOE, and thus an inspection apparatus does not need to perform a processof creating the temperature correction table 261, which allowing theplurality of oscillators 1 to be simultaneously manufactured. Therefore,it is not necessary to provide a large-scale manufacturing apparatus forindividually adjusting the oscillators 1 and not necessary to adjustvariations in characteristics of the temperature measurement unit 25 ofthe oscillator 1, and thus it is possible to reduce a manufacturing costof the oscillator 1.

1-2. Second Embodiment

Hereinafter, regarding an oscillator 1 according to a second embodiment,the same description as in the first embodiment will be omitted orsimplified, and only contents different from those in the firstembodiment will be mainly described. The structure of the oscillator 1according to the second embodiment is the same as that of the oscillator1 (FIGS. 1 to 3) according to the first embodiment, and thus theillustration and description thereof will not be repeated. FIG. 13 is afunctional block diagram of the oscillator 1 according to the secondembodiment. In FIG. 13, the same components as those in FIG. 4 will bedenoted by the same reference numerals and signs.

As illustrated in FIG. 13, in the oscillator 1 according to the secondembodiment, a temperature compensated oscillation circuit 2 isconfigured to further include a frequency division ratio calculationunit 28 in addition to the same components as those in the firstembodiment (FIG. 5).

In a case where a frequency division ratio corresponding to ameasurement value (temperature measurement value DT) obtained by atemperature measurement unit 25 is described in a temperature correctiontable 261, the frequency division ratio calculation unit 28 outputs thefrequency division ratio to a fractional N-PLL circuit 22. Specifically,the frequency division ratio calculation unit 28 calculates an addressADR of a storage unit 26 storing a frequency division ratiocorresponding to the temperature measurement value DT on the basis ofthe temperature measurement value DT, reads out the value of thefrequency division ratio in accordance with the calculated address ADR,and outputs the read-out value to the fractional N-PLL circuit 22.

In addition, in a case where a frequency division ratio corresponding tothe temperature measurement value DT is not described in the temperaturecorrection table 261, the frequency division ratio calculation unit 28calculates (approximate calculation) the frequency division ratiocorresponding to the temperature measurement value DT by using aplurality of frequency division ratios described in the temperaturecorrection table 261, and outputs the calculated frequency divisionratio to the fractional N-PLL circuit 22. For example, in a case where afrequency division ratio corresponding to the temperature measurementvalue DT is not described in the temperature correction table 261, thefrequency division ratio calculation unit 28 may perform approximatecalculation (complementary calculation) of the frequency division ratiocorresponding to the temperature measurement value DT by using afrequency division ratio corresponding to a temperature measurementvalue smaller than the temperature measurement value DT and a frequencydivision ratio corresponding to a temperature measurement value largerthan the temperature measurement value DT which are described in thetemperature correction table 261. Specifically, the frequency divisionratio calculation unit 28 calculates a plurality of addresses ADR of thestorage unit 26 storing a plurality of frequency division ratiosnecessary for the approximate calculation of the frequency divisionratio corresponding to the temperature measurement value DT on the basisof the temperature measurement value DT, sequentially reads out andacquires the values of the plurality of frequency division ratios storedin the calculated plurality of addresses ADR, performs approximatecalculation of the frequency division ratio corresponding to thetemperature measurement value DT by using the values of the plurality offrequency division ratios, and outputs the calculated frequency divisionratio to the fractional N-PLL circuit 22.

FIG. 14 is a diagram illustrating an example of the temperaturecorrection table 261 according to the second embodiment. In the exampleof FIG. 14, a correspondence relationship between a temperaturemeasurement value DT (0, 4, 8, . . . , 244, 248, and 252) of whichlow-order 2 bits in a 8-bit temperature measurement value DT (0 to 255)are all 0, an integer frequency division ratio N′ (X0, X4, X8, . . . ,X244, X248, and X252), and a fraction frequency division ratio F/M′ (Y0,Y4, Y8, . . . , Y244, Y248, and Y252) is described (stored). In short,the temperature correction table 261 of FIG. 14 is configured such thata correspondence relationship between the temperature measurement valueDT and the frequency division ratio is selected every fourth values andthe remaining values are thinned out, with respect to the temperaturecorrection table 261 of FIG. 7, and the address ADR (0 to 63) coincideswith a value of high-order 6 bits in the 8-bit temperature measurementvalue DT (0 to 255).

In this case, when low-order 2 bits of the 8-bit temperature measurementvalue DT are all 0, the frequency division ratio (the integer frequencydivision ratio N′ and the fraction frequency division ratio F/M′) whichcorresponds to the temperature measurement value DT is described in thetemperature correction table 261, and thus the frequency division ratiocalculation unit 28 reads out the value of the integer frequencydivision ratio N′ and the value of the fraction frequency division ratioF/M′ from the storage unit 26 (temperature correction table 261) byusing a value of high-order 6 bits in the temperature measurement valueDT as the address ADR, and outputs the read-out values to the fractionalN-PLL circuit 22 as an integer frequency division ratio N and a fractionfrequency division ratio F/M. For example, when the temperaturemeasurement value DT is 0, the frequency division ratio calculation unit28 reads out the value X0 of the integer frequency division ratio N′ andthe value Y0 of the fraction frequency division ratio F/M′ from thestorage unit 26 (temperature correction table 261), and outputs theread-out values to the fractional N-PLL circuit 22 as an integerfrequency division ratio N and a fraction frequency division ratio F/M.

In addition, when either or both of the low-order 2 bits of the 8-bittemperature measurement value DT are 1, since the frequency divisionratio (the integer frequency division ratio N′ and the fractionfrequency division ratio F/M′) which corresponds to the temperaturemeasurement value DT is not described in the temperature correctiontable 261, the frequency division ratio calculation unit 28 first readsout, for example, the value of the integer frequency division ratio N′and the value of the fraction frequency division ratio F/M′ from thestorage unit 26 (temperature correction table 261) by using a value ofhigh-order 6 bits of the temperature measurement value DT as the addressADR. Further, the frequency division ratio calculation unit 28repeatedly performs a process of reading out the value of the integerfrequency division ratio N′ and the value of the fraction frequencydivision ratio F/M′, for example, by increasing (decreasing) the valuesof the address ADR by a predetermined number, to thereby acquire apredetermined number of values of the integer frequency division ratioN′ and the fraction frequency division ratio F/M′. The frequencydivision ratio calculation unit 28 performs approximate calculation ofthe values of the integer frequency division ratio N and the fractionfrequency division ratio F/M corresponding to the temperaturemeasurement value DT by using the acquired predetermined number ofvalues of the integer frequency division ratio N′ and the fractionfrequency division ratio F/M′, and outputs the calculated values to thefractional N-PLL circuit 22. For example, in a case where frequencytemperature characteristics of the clock signal OSCCLK are shown as acubic curve (see FIG. 5), the frequency division ratio calculation unit28 reads out values X0, X4, and X8 of the integer frequency divisionratio N′ and values Y0, Y4, and Y8 of the fraction frequency divisionratio F/M′ from the addresses 0, 1, and 2 of the storage unit 26(temperature correction table 261) when the temperature measurementvalue DT is 3, specifies a cubic function in which a frequency divisionratio=X0+Y0 is established when the temperature measurement value DT=0,a frequency division ratio=X4+Y4 is established when the temperaturemeasurement value DT=4, a frequency division ratio=X8+Y8 is establishedwhen the temperature measurement value DT=8, performs approximatecalculation (complementary calculation) of the corresponding frequencydivision ratio (the integer frequency division ratio N and the fractionfrequency division ratio F/M) by the substitution of the temperaturemeasurement value DT=3 for the cubic function, and outputs thecalculated value to the fractional N-PLL circuit 22.

Meanwhile, in a case where the frequency division ratio corresponding tothe temperature measurement value DT is not described in the temperaturecorrection table 261, the frequency division ratio calculation unit 28may appropriately determine the predetermined number of values of theinteger frequency division ratio N′ and the fraction frequency divisionratio F/M′ which are acquired from the storage unit 26 (temperaturecorrection table 261) or the predetermined number of values of theaddress ADR which is increased (or decreased) in accordance with thefrequency temperature characteristics of the clock signal OSCCLK so thatthe values of the integer frequency division ratio N and the fractionfrequency division ratio F/M which are obtained by the approximatecalculation satisfy a sufficient level of accuracy.

A temperature correction table updating unit 27 performs a process ofupdating the temperature correction table 261 (temperature correctiontable updating process) on the basis of an output signal (clock signalPLLCLK) of the fractional N-PLL circuit 22 and a reference clock signalREFCLK which is input from the outside of the temperature compensatedoscillation circuit 2 in a temperature correction table update mode.Specifically, the temperature correction table updating unit 27calculates a frequency division ratio for bringing the frequency of theoutput signal (clock signal PLLCLK) of the fractional N-PLL circuit 22close to the frequency of the reference clock signal REFCLK only in acase where a frequency division ratio corresponding to the temperaturemeasurement value DT which is output by the temperature measurement unit25 is described in the temperature correction table 261 in thetemperature correction table update mode, and updates the temperaturecorrection table 261 on the basis of the frequency division ratio andthe temperature measurement value DT which is output by the temperaturemeasurement unit 25. Similarly to the first embodiment, also in thesecond embodiment, the reference clock signal REFCLK having asufficiently small frequency deviation with respect to a targetfrequency (sufficiently satisfying frequency accuracy required for theoscillator 1) is input from an external terminal OE of the oscillator 1(an OE terminal of the temperature compensated oscillation circuit 2) inthe temperature correction table update mode, and the ambienttemperature of the oscillator 1 gradually changes in a temperature range(for example, −45° C. to +90° C.) including an operation guaranteetemperature range (for example, −40° C. to +85° C.) of the oscillator 1,thereby causing the temperature correction table updating unit 27 toperform the temperature correction table updating process.

FIG. 15 is a flow chart illustrating an example of a procedure of atemperature correction table updating process performed by thetemperature correction table updating unit 27 according to the secondembodiment.

As illustrated in FIG. 15, when an operation mode of the oscillator 1(temperature compensated oscillation circuit 2) is set to be atemperature correction table update mode, the temperature correctiontable updating unit 27 first acquires the temperature measurement valueDT which is output by the temperature measurement unit 25 (S200).

Next, the temperature correction table updating unit 27 determines thatthe temperature correction table 261 is to be updated when a frequencydivision ratio corresponding to the temperature measurement value DTacquired in Step S200 is described in the temperature correction table,and determines that the temperature correction table is not to beupdated when a frequency division ratio corresponding to the temperaturemeasurement value DT acquired in Step S200 is not described (S210). Forexample, in a case where the temperature correction table 261 isconfigured as illustrated in FIG. 14, the temperature correction tableupdating unit 27 determines that the temperature correction table is tobe updated when the temperature measurement value DT acquired in StepS200 is any one of 0, 4, 8, . . . , 244, 248, and 252, and determinesthat the temperature correction table is not to be updated when thetemperature measurement value DT is a value other than the values.

In a case where the temperature correction table updating unit 27determines that the temperature correction table is not to be updated (Nof S210), the temperature correction table updating unit performs theprocess of step S200 again. In addition, in a case where the temperaturecorrection table updating unit 27 determines that the temperaturecorrection table is to be updated (Y of S210), the temperaturecorrection table updating unit compares a frequency f_(PLLCLK) of theclock signal PLLCLK with a frequency f_(REFCLK) of the reference clocksignal REFCLK (S220).

Next, the temperature correction table updating unit 27 calculates afrequency division ratio (an integer frequency division ratio N′ and afraction frequency division ratio F/M′) for bringing the frequencyf_(PLLCLK) of the clock signal PLLCLK close to the frequency f_(REFCLK)of the reference clock signal REFCLK, on the basis of a result of thecomparison between the frequencies which is performed in Step S220(S230).

Next, the temperature correction table updating unit 27 writes thefrequency division ratio (the integer frequency division ratio N′ andthe fraction frequency division ratio F/M′), which is calculated in StepS230, in the storage unit 26 in association with the temperaturemeasurement value DT acquired in Step S200 to thereby update thetemperature correction table 261 (S240).

The temperature correction table updating unit 27 continuously performsthe processes of Steps S200 to S240 while the temperature correctiontable update mode is continued (Y of S250), and terminates the processeswhen the temperature correction table update mode is terminated (N ofS250).

Meanwhile, in the flow chart of FIG. 15, a portion of the processes ofSteps S200 to S250 may be appropriately omitted or changed, or otherprocesses may be added. In addition, in the flow chart of FIG. 15, theorder of the processes of Steps S200 to S250 may be changed in apossible range.

A method of manufacturing an oscillator of the second embodiment may bethe same as that of the first embodiment (FIG. 11), and thus theillustration and description of the flowchart will not be repeated.

The above-described oscillator 1 according to the second embodimentexhibits the same operational effects as those of the oscillator 1according to the first embodiment. Further, in the oscillator 1according to the second embodiment, approximate calculation of afrequency division ratio corresponding to a temperature measurementvalue DT, which is not described in the temperature correction table261, is performed in the temperature compensated oscillation circuit 2,and thus it is possible to reduce the size of the temperature correctiontable 261. Therefore, according to the second embodiment, it is possibleto further reduce a manufacturing cost of the oscillator.

1-3. Modification Example

For example, the oscillator 1 according to the first embodiment or thesecond embodiment is an oscillator having a temperature compensationfunction (TCXO and the like), but may be an oscillator having afrequency control function together with a temperature compensationfunction (voltage controlled temperature compensated crystal oscillator(VC-TCXO) and the like), or the like.

2. Electronic Apparatus

FIG. 16 is a functional block diagram illustrating an example of aconfiguration of an electronic apparatus according to this embodiment.In addition, FIG. 17 is a diagram illustrating an example of theexterior of a smartphone which is an example of an electronic apparatusaccording to this embodiment.

An electronic apparatus 300 according to this embodiment is configuredto include an oscillator 310, a central processing unit (CPU) 320, anoperation unit 330, a read only memory (ROM) 340, a random access memory(RAM) 350, a communication unit 360, and a display unit 370. Meanwhile,the electronic apparatus according to this embodiment may be configuredsuch that a portion of components (respective units) of FIG. 16 isomitted or changed or other components are added.

The oscillator 310 includes a temperature compensated oscillationcircuit 312 and a resonator 313. The temperature compensated oscillationcircuit 312 oscillates the resonator 313 to generate an oscillationsignal. The oscillation signal is output to the CPU 320 from an externalterminal of the oscillator 310.

The CPU 320 is a processing unit that performs various calculationprocesses or a control process by using the oscillation signal which isinput from the oscillator 310 as a clock signal, in accordance withprograms stored in the ROM 340 and the like. Specifically, the CPU 320performs various processes based on an operation signal received fromthe operation unit 330, a process of controlling the communication unit360 in order to perform data communication with an external device, aprocess of transmitting a display signal for displaying various piecesof information on the display unit 370, and the like.

The operation unit 330 is an input device constituted by operation keys,button switches or the like, and outputs an operation signalcorresponding to a user's operation to the CPU 320.

The ROM 340 is a storage unit that stores programs, data, and the likefor causing the CPU 320 to perform various calculation processes andcontrol processes.

The RAM 350 is a storage unit which is used as a work area of the CPU320 and temporarily stores programs or data which is read out from theROM 340, data which is input from the operation unit 330, results ofcomputation executed by the CPU 320 in accordance with various programs,and the like.

The communication unit 360 performs a variety of control forestablishing data communication between the CPU 320 and an externaldevice.

The display unit 370 is a display device constituted by a liquid crystaldisplay (LCD) and the like, and displays various pieces of informationon the basis of a display signal which is input from the CPU 320. Thedisplay unit 370 may be provided with a touch panel functioning as theoperation unit 330.

The CPU 320 can perform various processes on the basis of an oscillationsignal having a small frequency deviation (high frequency accuracy) byapplying, for example, the oscillators 1 according to theabove-described embodiments as the oscillator 310 or applying thetemperature compensated oscillation circuits 2 according to theabove-described embodiments as the temperature compensated oscillationcircuit 312, and thus it is possible to realize the electronic apparatuswith high reliability.

Various electronic apparatuses are considered as the electronicapparatus 300, and examples of the electronic apparatus include apersonal computer (for example, mobile-type personal computer, laptoppersonal computer, or tablet personal computer), a mobile terminal suchas a smart phone or a cellular phone, a digital still camera, an ink jetejecting apparatus (for example, ink jet printer), a storage areanetwork device such as a router or a switch, a local area networkdevice, a device for a vehicle terminal base station, a television, avideo camera, a video recorder, a car navigation device, a real-timeclock device, a pager, an electronic notebook (also including acommunication function), an electronic dictionary, an electroniccalculator, an electronic game console, a game controller, a wordprocessor, a workstation, a TV phone, a security TV monitor, electronicbinoculars, a POS terminal, a medical instrument (for example,electronic thermometer, sphygmomanometer, blood glucose monitoringsystem, electrocardiogram measurement device, ultrasound diagnosticdevice, and electronic endoscope), a fish finder, various types ofmeasuring apparatuses, meters and gauges (for example, meters and gaugesof a vehicle, an aircraft, and a vessel), a flight simulator, a headmounted display, a motion tracer, a motion tracker, a motion controller,PDR (pedestrian position and direction measurement), and the like.

An example of the electronic apparatus 300 according to this embodimentis a transmission device functioning as a device for a terminal basestation which communicates with a terminal in a wired or wirelessmanner, and the like by using the oscillator 310 mentioned above as areference signal source. For example, the oscillators 1 according to theabove-described embodiments are applied as the oscillator 310, and thusit is also possible to realize the electronic apparatus 300, required tohave high frequency accuracy, high performance, and high reliability,which is usable in, for example, a communication base station and thelike at a lower cost than in the related art.

In addition, another example of the electronic apparatus 300 accordingto this embodiment may be a communication device including a frequencycontrol unit in which the communication unit 360 receives an externalclock signal and the CPU 320 (processing unit) controls the frequency ofthe oscillator 310 on the basis of the external clock signal and anoutput signal (internal clock signal) of the oscillator 310. Thecommunication device may be a backbone network apparatus such as astratum 3, or a communication apparatus which is used in a femtocell.

3. Vehicle

FIG. 18 is a diagram (top view) illustrating an example of a vehicleaccording to this embodiment. A vehicle 400 illustrated in FIG. 18 isconfigured to include an oscillator 410, controllers 420, 430, and 440that perform a variety of control of an engine system, a brake system, akeyless entry system and the like, a battery 450, and a backup battery460. Meanwhile, the vehicle according to this embodiment may beconfigured such that a portion of components (respective units) of FIG.18 is omitted or changed or other components are added.

The oscillator 410 includes a temperature compensated oscillationcircuit and a resonator which are not shown in the drawing, and thetemperature compensated oscillation circuit oscillates the resonator togenerate an oscillation signal. The oscillation signal is output to thecontrollers 420, 430, and 440 from an external terminal of theoscillator 410, and is used as, for example, a clock signal.

The battery 450 supplies power to the oscillator 410 and the controllers420, 430, and 440. The backup battery 460 supplies power to theoscillator 410 and the controllers 420, 430, and 440 when an outputvoltage of the battery 450 becomes lower than a threshold value.

The controllers 420, 430, and 440 can perform a variety of control onthe basis of an oscillation signal having a small frequency deviation(high frequency accuracy), for example, by applying the oscillators 1according to the above-described embodiments as the oscillator 410 orapplying the temperature compensated oscillation circuit 2 according tothe above-described embodiments as a temperature compensated oscillationcircuit included in the oscillator 410, and thus it is possible torealize the vehicle with high reliability.

Various vehicles are considered as the vehicle 400, and examples of thevehicle include an automobile (including an electric automobile), anaircraft such as a jet engine airplane or a helicopter, a vessel, arocket, a satellite, and the like.

The invention is not limited to this embodiment, and variousmodifications can be made without departing from the scope of theinvention.

The above-described embodiments and modification example are justexamples, and are not limited thereto. For example, the embodiments andmodification can be appropriately combined with each other.

The invention includes configurations (for example, configurationshaving the same functions, methods and results, or configurations havingthe same objects and effects) which are substantially the same as theconfigurations described in the above embodiments. In addition, theinvention includes configurations in which non-essential elements of theconfigurations described in the embodiments are replaced. In addition,the invention includes configurations exhibiting the same operations andeffects as, or configurations capable of achieving the same objects as,the configurations described in the embodiments. In addition, theinvention includes configurations that known techniques are added to theconfigurations described in the embodiments.

The entire disclosure of Japanese Patent Application No. 2016-113223,filed Jun. 7, 2016 is expressly incorporated by reference herein.

What is claimed is:
 1. A temperature compensated oscillation circuitcomprising: an oscillation circuit that oscillates a resonator; afractional N-PLL circuit that multiplies frequency of an oscillationsignal which is output by the oscillation circuit, on the basis of afrequency division ratio which is input; a temperature measurement unitthat measures temperature; and a storage unit that stores a temperaturecorrection table for correcting frequency temperature characteristics ofthe oscillation signal, wherein the frequency division ratio of thefractional N-PLL circuit is set on the basis of a measurement valueobtained by the temperature measurement unit and the temperaturecorrection table.
 2. The temperature compensated oscillation circuitaccording to claim 1, further comprising: a terminal; a control unitthat is capable of setting an update mode for updating the temperaturecorrection table; and a temperature correction table updating unit thatupdates the temperature correction table in the update mode on the basisof an output signal of the fractional N-PLL circuit and a referenceclock signal which is input from the terminal.
 3. The temperaturecompensated oscillation circuit according to claim 2, wherein thetemperature correction table updating unit calculates the frequencydivision ratio for bringing frequency of the output signal of thefractional N-PLL circuit close to frequency of the reference clocksignal in the update mode, and updates the temperature correction tableon the basis of the frequency division ratio.
 4. The temperaturecompensated oscillation circuit according to claim 1, furthercomprising: a frequency division ratio calculation unit that calculatesthe frequency division ratio corresponding to the measurement valueobtained by the temperature measurement unit by using a plurality of thefrequency division ratios described in the temperature correction table,in a case where the frequency division ratio corresponding to themeasurement value is not described in the temperature correction table.5. The temperature compensated oscillation circuit according to claim 2,further comprising: a frequency division ratio calculation unit thatcalculates the frequency division ratio corresponding to the measurementvalue obtained by the temperature measurement unit by using a pluralityof the frequency division ratios described in the temperature correctiontable, in a case where the frequency division ratio corresponding to themeasurement value is not described in the temperature correction table.6. The temperature compensated oscillation circuit according to claim 3,further comprising: a frequency division ratio calculation unit thatcalculates the frequency division ratio corresponding to the measurementvalue obtained by the temperature measurement unit by using a pluralityof the frequency division ratios described in the temperature correctiontable, in a case where the frequency division ratio corresponding to themeasurement value is not described in the temperature correction table.7. An oscillator comprising: the temperature compensated oscillationcircuit according to claim 1; and the resonator.
 8. An oscillatorcomprising: the temperature compensated oscillation circuit according toclaim 2; and the resonator.
 9. An oscillator comprising: the temperaturecompensated oscillation circuit according to claim 3; and the resonator.10. An oscillator comprising: the temperature compensated oscillationcircuit according to claim 4; and the resonator.
 11. An electronicapparatus comprising the oscillator according to claim
 5. 12. Anelectronic apparatus comprising the oscillator according to claim
 6. 13.An electronic apparatus comprising the oscillator according to claim 7.14. An electronic apparatus comprising the oscillator according to claim8.
 15. A vehicle comprising the oscillator according to claim
 5. 16. Avehicle comprising the oscillator according to claim
 6. 17. A vehiclecomprising the oscillator according to claim
 7. 18. A vehicle comprisingthe oscillator according to claim
 8. 19. A method of manufacturing anoscillator, the method comprising: assembling the oscillator thatincludes a terminal, a resonator, and a temperature compensatedoscillation circuit, the temperature compensated oscillation circuitbeing provided with an oscillation circuit that oscillates theresonator, a fractional N-PLL circuit that multiplies frequency of anoscillation signal which is output by the oscillation circuit on thebasis of a frequency division ratio which is input, a temperaturemeasurement unit that measures temperature, a storage unit that stores atemperature correction table for correcting frequency temperaturecharacteristics of the oscillation signal, a control unit that iscapable of setting an update mode for updating the temperaturecorrection table, and a temperature correction table updating unit thatupdates the temperature correction table on the basis of an outputsignal of the fractional N-PLL circuit and a reference clock signalwhich is input from the terminal, and the frequency division ratio ofthe fractional N-PLL circuit being set on the basis of a measurementvalue obtained by the temperature measurement unit and the temperaturecorrection table; setting the temperature compensated oscillationcircuit to be in the update mode; and inputting the reference clocksignal to the terminal to thereby change temperature of the oscillatorin a predetermined range.